Dielectric materials are frequently used in the formation of integrated circuit devices. Dielectric materials are used to form gate oxides for metal oxide semiconductor field effect transistors (MOSFETs), capacitor dielectrics, inter-polysilicon dielectrics, inter-metal dielectrics, final passivation layers, sacrificial layers, masking layers, and like structures. In most cases, the most critical oxide in an integrated circuit device is the gate oxide.
There are two conventional and widely used methods of forming a gate oxide. Both methods of forming the gate oxide require exposure of a silicon material to an oxidant-containing ambient and elevation of an ambient temperature. A wet silicon dioxide is formed over the silicon material when using steam, and a dry silicon dioxide material is formed when using oxygen. Wet and dry oxides are used frequently to form gate oxides. Silicon dioxide materials have several known disadvantages, such as boron penetration between a gate and a channel region, hot carrier injection problems, and a defect density and micropores which cause reduced breakdown voltages and reduced transistor lifetime.
Alternatively, another method of forming a gate oxide uses either nitrogen-containing or flourine-containing ambient in conjunction with the oxygen-containing ambient during the oxidation step to form a gate oxide having either nitrogen or fluorine therein to improve the quality of the gate oxide. However, a nitrided gate oxide lowers the peak transconductance (Gm) at a low electric field while increasing the transconductance at a high electric field. A higher Gm translates to a faster device speed which is more desirable.
A paper by James Cable et al. entitled "Improvements in Rapid Thermal Oxide/Re-Oxidized Nitrided Oxide (ONO) Films using NF.sub.3 " in the Materials Research Society Symposium Proceedings Vol. 224 postulated the combined effects of nitrogen and fluorine for improving the interface hardness between Si and SiO.sub.2 to guard against hot electron and radiation damage. The process involved a substrate preclean step in NF.sub.3 to introduce fluorine into the substrate, followed by a later exposure to NH.sub.3 during the oxidation process to introduce nitrogen into the substrate. Cable's study indicated that low net charge trapping might be achievable given the right processing sequence. However, Cable's method was admittedly difficult to control and therefore, not suitable for a manufacturing environment.
Thus, a need exists for a controllable process to form a gate oxide having both nitrigen and fluorine therein to take advantage of the benefits that each provides.